Original route to polylactide-polystyrene diblock copolymers containing a sulfonyl group at the junction between both blocks as precursors to functional nanoporous materials

Article abstract of DOI:10.1016/j.reactfunctpolym.2012.04.012

Novel functionalized nanoporous polymeric materials could be derived from poly(D,L-lactide)-block-polystyrene (PLA-b-PS) diblock copolymers with a sulfonyl group at the junction between both blocks were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) using a synthetic difunctional initiator through a three-step sequential methodology. Different ω-bromo PLA polymers with various molar masses ranging from 3640 to 11,440 g mol^-1 were first produced by coupling ω-hydroxy PLA precursors to a chlorosulfonyl- functionalized ATRP initiator previously prepared, thus leading to the formation of suitable macroinitiators for the subsequent ATRP polymerization of styrene. Consequently, PLA-b-PS diblock copolymers were obtained with a finely tuned PLA volume fraction (f_PLA) in order to develop a microphased-separation morphology. The resulting copolymers as well as the intermediate compounds were carefully analyzed by size exclusion chromatography and ¹H NMR. Upon shear flow induced by a channel die processing, oriented copolymers were generally afforded as characterized by small-angle-X-ray scattering (SAXS). Such copolymers were finally submitted to mild alkaline conditions so as to hydrolyze the sacrificial PLA block, and the presence of the sulfonic acid functionality on the pore walls of the resulting nanoporous materials was evidenced by means of a post-modification reaction consisting in the corresponding sulfonamide formation.

Full text of DOI:10.1016/j.reactfunctpolym.2012.04.012

Reactive & Functional Polymers 72 (2012) 495–502
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Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Original route to polylactide–polystyrene diblock copolymers containing
a sulfonyl group at the junction between both blocks as precursors to functional
nanoporous materials
Rim Majdoub a,b, Tarek Antoun a, Benjamin Le Droumaguet a, Mourad Benzina b, Daniel Grande a,
⇑
a Institut de Chimie et des Matériaux Paris-Est, UMR 7182, CNRS-Université Paris-Est Créteil Val-de-Marne, 2, rue Henri Dunant, 94320 Thiais, France
b Laboratoire ‘‘Eau, Energie et Environnement’’, Ecole Nationale d’Ingénieurs de Sfax, Université de Sfax, 3038 Sfax, Tunisia
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel functionalized nanoporous polymeric materials could be derived from poly(D,L-lactide)-block-
polystyrene (PLA-b-PS) diblock copolymers with a sulfonyl group at the junction between both blocks
were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical poly-
merization (ATRP) using a synthetic difunctional initiator through a three-step sequential methodology.
Received 25 March 2012
Accepted 25 April 2012
Available online 7 May 2012
Different
first produced by coupling
x
-bromo PLA polymers with various molar masses ranging from 3640 to 11,440 g molÀ1 were
Keywords:
x-hydroxy PLA precursors to a chlorosulfonyl-functionalized ATRP initiator
Semi-hydrolyzable diblock copolymers
Sulfonyl-functionalized junction point
Ring-opening polymerization/atom transfer
radical polymerization tandem approach
Selective hydrolysis
previously prepared, thus leading to the formation of suitable macroinitiators for the subsequent ATRP
polymerization of styrene. Consequently, PLA-b-PS diblock copolymers were obtained with a finely tuned
PLA volume fraction (fPLA) in order to develop a microphased-separation morphology. The resulting
copolymers as well as the intermediate compounds were carefully analyzed by size exclusion chromatog-
raphy and 1H NMR. Upon shear flow induced by a channel die processing, oriented copolymers were
generally afforded as characterized by small-angle-X-ray scattering (SAXS). Such copolymers were finally
submitted to mild alkaline conditions so as to hydrolyze the sacrificial PLA block, and the presence of the
sulfonic acid functionality on the pore walls of the resulting nanoporous materials was evidenced by
means of a post-modification reaction consisting in the corresponding sulfonamide formation.
Ó 2012 Elsevier Ltd. All rights reserved.
Functional nanoporous materials
1. Introduction
ular, block copolymers are versatile hybrid macromolecules that
have been used as nanostructured precursors for the generation
Over the last decade, porous polymeric materials displaying
finely tuned and regular pore sizes have been extensively investi-
gated due to their diverse applications in many research fields,
e.g. supports for catalysis or gas storage, separation, and filtration
[1,2], as well as biosensors or biomedical devices [3,4]. In this rap-
idly expanding field, researchers have particularly focused their
investigation on the control of pore size and pore size distribution
[5]. Another important feature of these porous materials that has
to be taken carefully into account relies on the proper selection
and positioning of chemical functions that line the pore walls,
regarding the potential applications further considered. Indeed,
the functional group should be appropriately placed without the
need to require to tedious post-polymerization functionalization
strategies.
of a wide variety of nanoporous materials [6]. Indeed, the
incompatibility of distinct macromolecular segments in diblock
copolymers leads to their nanoscopic self-organization, and as a
consequence to their potential utilization as structure directing
agents [7]. For instance, it has been shown that self-organized
block copolymers can lead to the formation of well-defined nano-
structures in which the morphology and domain sizes are tunable
on the nanoscopic length scale. In this regard, a classical example
was given by Hillmyer’s group [6] that showed that AB diblock
copolymers comprising two-thirds of A monomer and one-third
of B monomer, and that displays high enough overall molar mass,
form long cylinders of B with nanometer-scale (5–50 nm) diame-
ters that organize on a hexagonal lattice within a continuous A
matrix. Unfortunately, the effects of polydispersity on the order–
disorder transition have potential implications on the morphology
of block copolymers. Especially, domain spacing increases as the
polydispersity index (PDI) increases, and the PDI increase in one
block of an asymmetric diblock copolymer results in transitions
to morphologies with increased mean interfacial curvature toward
that block [8,9].
For many years, block copolymers have represented fascinating
macromolecular architectures in different research areas. In partic-
⇑
Corresponding author. Tel.: +33 (0)1 49 78 11 77; fax: +33 (0)1 49 78 12 08.
E-mail address: grande@icmpe.cnrs.fr (D. Grande).
1381-5148/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.reactfunctpolym.2012.04.012

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R. Majdoub et al. / Reactive & Functional Polymers 72 (2012) 495–502
The preparation of (co)polymers from multifunctional initiators
(2) were synthesized by ring-opening polymerization (ROP) of
D,L-lactide initiated by the butanol/tin(II) octanoate system
according to a literature procedure [15].
is also an area of intense research as it enables the generation of
telechelic (co)polymers that can undergo further post-polymeriza-
tion modifications [10–12]. Recently, one of our groups [13,14]
successfully demonstrated that the positioning of a particular func-
tional group between the two distinct blocks of semi-degradable
diblock copolymers can lead to the formation of novel functional-
ized nanoporous materials. By employing an asymetric difunc-
tional initiator suitable for two distinct polymerization
mechanisms, i.e. atom transfer radical polymerization (ATRP) of
styrene and ring-opening polymerization (ROP) of lactide, polysty-
rene-block-poly(D,L-lactide (PS-b-PLA) copolymers were obtained.
The orientation of the resulting copolymers, followed by the
hydrolysis of the PLA sacrificial block, could afford highly ordered
arrays of nanochannels with varying pore diameters and a carbox-
ylic acid functionality lining the nanochannel walls.
In continuation of our recent efforts on the direct and straight-
forward generation of functionalized nanoporous polymers, we re-
port on an original three-step methodology to synthesize PLA-b-PS
copolymers possessing a sulfonyl group at the junction point be-
tween both blocks. Their macroscopic orientation and the subse-
quent hydrolysis of the sacrificial PLA block leads to the
formation of porous polymeric materials decorated with a sulfonic
acid functionality in the inner part of the nanochannels. The pres-
ence of this particular functionality was proved via a post-modifi-
cation reaction during which sulfonic acid groups were
transformed into sulfonamide functions upon reaction with a small
aliphatic amine.
D,L-lactide, 4-isopropylbenzenesulfonyl chloride (97%), bro-
mine (Br2, P99.5%) pentamethyldiethylenetriamine (PMDETA,
99%), tin(II) 2-ethylhexanoate (Sn(Oct)2, ꢀ95%) and 2-methoxyeth-
ylamine (99%) were purchased from Aldrich and used as received.
CuBr (99%, Aldrich) was stirred in glacial acetic acid, washed with
MeOH, and dried under vacuum at room temperature. Styrene
(P99%, Aldrich) was stirred over KOH, and distilled over CaH2
under vacuum just before use. Triethylamine (99%, Aldrich) was
stirred in the presence of KOH at 70 °C during 12 h and distilled
under argon. Anisole (99%, SDS, France) was dried over sodium/
benzophenone overnight at 90 °C and distilled under vacuum.
Dichloromethane was dried over CaH2 and distilled under argon.
Anhydrous toluene, CCl4 and methanol with the highest purity
grade were purchased from SDS and used as received.
2.2. Synthesis of the chlorosulfonyl-functionalized ATRP initiator (1)
A solution of bromine (2.9 g, 1.82 Â 10À2 mol) in 16 mL of
carbon tetrachloride was dropwise added to a refluxing solution
of 4-isopropylbenzene sulfonyl chloride (3.98 g, 1.82 Â 10À2 mol)
dissolved in 16 mL of carbon tetrachloride [16]. The reaction mix-
ture was finally refluxed for 10 min and the solvent was evapo-
rated under reduced pressure. The product was then washed
with water and dried overnight under reduced pressure to give
the desired brominated product 1 as a white solid (yield = 96%).
1H NMR (CDCl3, 400 MHz, 298 K) d (ppm): 2.22 (s, 6H, CH3), 7.86
(d, 2H, CHaromatic, J = 8.8 Hz), 8.01 (d, 2H, CHaromatic, J = 8.8 Hz); 13C
NMR (CDCl3, 100 MHz, 298 K) d (ppm) 35.3 (2C, C–(CH3)2), 60.8
(1C, C–Br), 127.3, 127.5, 143.4 (1C, C–SO2Cl), 154.5 (5C, Carom); FTIR
2. Experimental section
2.1. Materials
m
(cmÀ1): 577 (C–Br), 1174 and 1370 (SO2); elementary analysis:
All polymerizations were performed using standard Schlenk
exp C (36.09%), H (3.01%), Cl (11.96%), S (10.32%), O (10.48%), Br
(28.14%), theor (36.3%), H (3.4%), Cl (11.9%), S (10.7%), O (10.8%),
Br (26.9%).
techniques under argon atmosphere.
x
-hydroxy PLA precursors
CCl4 Br2,
reflux
O
S
O
S
Br
1
st step
Cl
Cl
Cl
Table 1
O
O
Molecular characteristics of
initiated by butanol.
x-hydroxy PLA (2) precursors synthesized by ROP of LA
Mn (SEC-RI) PDIc Mn (1H NMR) Yielde
b
c
d
Precursor
PLAn
Mn
O
(theoretical)
(g molÀ1
)
(g molÀ1
)
(%)
a
O
S
O
Br
O
+
H
(g molÀ1
)
O
n
PLA46 (2a)
PLA96 (2b)
PLA154 (2c) 8060
3030
6840
4600
8800
10,000
1.23
1.40
1.40 11,200
3380
6980
80
94
74
CH2Cl2,
reflux,
NEt3
2
nd step
n: number-average degree of polymerization of PLA as determined by 1H NMR.
a
b
c
M
n,theor = conversion  (2[LA]0/[initiator]0)  72 + Mn (end groups).
O
O
S
Obtained from SEC equipped with RI detection (PS standards) eluting with THF
Br
O
as the mobile phase.
O
d
Actual molar mass as calculated by 1H NMR from PLA.
O
n
e
Conversion as determined by gravimetry for ROP of lactide initiated by butanol.
CuBr,
PMDETA
anisole,
110°C
ATRP
3
rd step
Table 2
Characteristics of
x-bromo PLA-based macroinitiators (3).
a
b
Macroinitiator
PLAn-Br (3)
PLAn
Mn
Yield
(%)
Functionalization yield
(1H NMR) (%)
O
O
S
O
(g molÀ1
)
Br
m
O
PLA46_Br (3a)
PLA96_Br (3b)
PLA154_Br (3c)
PLA46
PLA96
PLA154 11,440
3640
7240
68
60
78
54
89
66
O
n
a
n: number-average degree of polymerization of PLA as determined by 1H NMR.
Fig. 1. Synthetic strategy adopted for the preparation of PLA-b-PS diblock copoly-
mers containing a sulfonyl group at the junction between both blocks.
b
Molar mass of PLA as determined by 1H NMR.

R. Majdoub et al. / Reactive & Functional Polymers 72 (2012) 495–502
497
2.3. Synthesis of
x
-bromo PLA macroinitiators (3)
resulting macroinitiator was precipitated in diethyl ether to re-
move the excess of the unreacted initiator 1. The obtained macro-
initiator 3b was dried under vacuum (yield = 60%). The
functionalization yield was evaluated by 1H NMR to be equal to
89%.
The sulfonyl chloride group of the initiator 1 was reacted with
the hydroxyl terminus of the previously synthesized PLA polymers
(2) to provide
x-bromo PLA macroinitiators (3). A typical synthesis
is described next. The PLA96 sample (2b) (5 g, 7.16 Â 10À4 mol) was
freeze-dried from toluene overnight under vacuum prior to the
2.4. Synthesis of PS-b-PLA diblock copolymers
reaction. The chlorosulfonyl-functionalized initiator
1 (0.61 g,
2 Â 10À3 mol) dissolved in 5 mL of distilled dichloromethane was
added, dropwise and under argon, to the PLA dissolved in 20 mL
of dichloromethane in the presence of triethylamine (0.199 g,
1.4 Â 10À3 mol) [17]. The reaction mixture was stirred for 48 h at
room temperature, and then 4 h at 40 °C. The product was washed
twice with water to remove the salts and the hydrolyzed propor-
tion of the initiator. The organic layer was concentrated, and the
PS-b-PLA diblock copolymers with a sulfonyl group at the junc-
tion between both blocks were prepared by atom transfer radical
polymerization (ATRP) of styrene initiated by ternary systems con-
stituted of PLA macroinitiators, CuBr, and PMDETA, at 110 °C for
18 h in anisole. In a typical experiment, the macroinitiator 3a
(1.74 g, 2.4 Â 10À4 mol) and CuBr (0.03 g, 2 Â 10À4 mol) were
introduced into an oven-dried Schlenk tube. Styrene (3.23 g,
Fig. 2. 1H NMR spectrum of PLA96 precursor (2b).
Fig. 3. 1H NMR of PLA96-Br macroinitiator (3b).

498
R. Majdoub et al. / Reactive & Functional Polymers 72 (2012) 495–502
3.1 Â 10À2 mol) and PMDETA (51
l
L, 2.4 Â 10À4 mol) were added
H2O = 40/60 vol.%) at 65 °C for 5–7 days. The obtained porous sam-
ples were washed abundantly with water and methanol, then
vacuum-dried at room temperature.
under argon. The reagents were diluted with 5 mL of anisole, and
the flask was submitted to three freeze–pump–thaw cycles. The
polymerization was triggered by immersion of the flask in an oil
bath at 110 °C. After 80 h, the obtained diblock copolymer 4a
was precipitated in methanol to remove the PLA fraction non-func-
tionalized with a bromide moiety.
2.8. End-group functionalization
In a first step, 4.48 lL of thionyl chloride dissolved in 1 mL of
dichloromethane was dropwise added to 82 mg (2.06 Â 10À6 mol)
2.5. Homopolymerization of styrene from initiator 1
of the mesoporous PS sample (Mn ꢀ 4000 g molÀ1) dissolved in
4 mL of dichloromethane in the presence of 12.5 lL of triethyl-
The initiator 1 (20 mg, 6.72 Â 10À5 mol) and CuBr (9.6 mg,
6.72 Â 10À5 mol) were introduced into an oven-dried flask. Styrene
amine (9.27 Â 10À5 mol) under argon at 0 °C. The reaction mixture
was stirred for 48 h at room temperature and was used without
any further purification. In the second step, 1.85 mg (2.45 Â
10À5 mol) of 2-methoxyethylamine in 1 mL dichloromethane was
dropwise added into the previous mixture in the presence of
(2.09 g, 2 Â 10À2 mol) and PMDETA (16.8
l
L, 8 Â 10À5 mol) were
added under argon atmosphere. The reagents were diluted with
5 mL of anisole before submitting the polymerization feed to three
freeze–pump–thaw cycles. The polymerization was finally
triggered by immersion of the flask into an oil bath at 110 °C. Three
samples were withdrawn during the polymerization course at
t = 14, 24 and 86 h in order to determine Mn and PDI values of
the as-obtained PS homopolymers.
4.3
l
L (3.09 Â 10À5 mol) of triethylamine at 0 °C. After stirring
the reaction mixture overnight, the polymer was precipitated sev-
eral times in methanol, then dried under vacuum. 1H NMR analysis
was used to determine the ratio of sulfonic acid groups that were
converted into the corresponding sulfonamide functions (function-
alization yield close to 100%).
2.6. Orientation of PS-b-PLA diblock copolymers
A home-made channel die (3 mm wide and 60 mm long) was
used to align the nanodomains in the block copolymers. Previously
pressed pieces of PS-b-PLA were placed in the center of the channel
die which was then heated to 120 °C in a laboratory press. The
samples were subjected to compression upon constant load
(compression ratio of ꢀ10) and quenched under load to room tem-
perature over a period of 1 h. The samples were post-annealed
overnight at 160 °C before removing them from the channel die
with a sample thickness between 0.5 and 1.0 mm.
2.9. Instrumentation
Size exclusion chromatography (SEC) was performed on a sys-
tem equipped with a Spectra Physics P100 pump, two PL gel
5 lm mixed-C columns (Polymer Laboratories), and a Shodex RI
71 refractive index detector. The mobile phase was tetrahydrofu-
ran at a flow rate of 1 mL minÀ1. Calibration curves were obtained
with polystyrene standards obtained from Polymer Laboratories.
1H and 13C NMR spectra were recorded at room temperature on
a
Bruker Avance II spectrometer operating at a resonance
2.7. Hydrolysis of PLA block in PS-b-PLA diblock copolymers
frequency of 400 and 100 MHz respectively. For 1H NMR analysis,
the sample concentration was ꢀ10 mg mLÀ1
, while it was
In order to selectively degrade the sacrificial PLA block, the dif-
ferent PS-b-PLA samples were immersed in a mixture containing
methanol and a 0.5 mol LÀ1 NaOH aqueous solution (MeOH/
ꢀ30 mg mLÀ1, for 13C NMR experiments. CDCl3 was used as solvent
and internal standard (7.26 ppm in 1H NMR; 77.2 ppm in 13C
NMR).
Fig. 4. 1H NMR of PLA96-b-PS91 diblock copolymer (4b) before hydrolysis.

R. Majdoub et al. / Reactive & Functional Polymers 72 (2012) 495–502
499
Table 3
Molecular features of PLA-b-PS copolymers (4).
b
c
d
f
Copolymer
Mn
Mn
PDIc Mn
Yielde fPLA
(1H NMR) (%)
a
PLAn-b-PSm (4) (theoretical)
(SEC-RI)
(g molÀ1
8220
]
(g molÀ1
)
(g molÀ1
8430
)
PLA46-b-PS46
(4a)
PLA96-b-PS91
(4b)
PLA154-b-PS240
(4c)
13,100
23,300
87,000
1.44
88
95
92
0.37
17,100
30,500
1.62 16,700
1.58 36,400
0.38
0.27
a
n,m: number-average degrees of polymerization of PLA and PS blocks as
determined by 1H NMR.
b
Mn,theor = [conversion  ([S]0/[macroinitiator]0)  104] + Mn (PLA-Br).
c
Obtained from SEC equipped with RI detection (PS standards) eluting with THF
as the mobile phase.
d
Actual molar mass as calculated by 1H NMR from macroinitiator (PLA block) and
PS block.
e
Conversion as determined by gravimetry for ATRP of styrene initiated by the
Fig. 5. SEC traces of PLA96-Br macroinitiator (3b, solid line) and corresponding
PLA96-b-PS91 copolymer (4b, dotted line).
different macroinitiators.
f
Volume fraction of PLA as calculated by 1H NMR, assuming that the densities of
PS and PLA are 1.02 and 1.25, respectively.
FTIR spectra were recorded on a Bruker Tensor 27 DTGS spec-
trometer in attenuated total reflection (ATR) mode between 4000
and 450 cmÀ1 by averaging 32 consecutive scans with a resolution
Table 4
of 4 cmÀ1
.
Molecular features of polystyrene samples obtained by ATRP of styrene using
The small-angle X-ray scattering (SAXS) experiments were per-
formed on a laboratory setup described in details elsewhere [18]. It
consists of a rotating Cu anode generator (Rigaku), graded layer Ni/
C mirror optics (Osmic), vacuum tubes (inserted between the sam-
ple and the detector), and a CCD camera (Princeton) with typical
exposure times ranging from 1 to 10 min. This setup allowed us
functional initiator 1.
Timeb
(h)
Mn (theoretical)
Mn (SEC-RI)
PDId Yielde
(%)
c
d
Polymer
PSm
(g molÀ1
)
(g molÀ1
)
a
PS83 (5a)
14
8960
13,280
30,900
27,700
36,800
40,000
1.87
1.75
29
43
PS124 (5b) 24
PS294 (5c) 86
1.74 100
to probe the 0.1–2.0 nmÀ1 q-range, where q = (4
p/k)sinh is the
a
b
c
m: theoretical number-average degree of polymerization of PS sample.
Duration of the reaction of polymerization.
scattering vector modulus, k = 0.1541 nm is the X-ray wavelength,
and 2h is the scattering angle. The two-dimensional (2-D) patterns
were analyzed with the Image software (Orsay, France).
Scanning Electron Microscopy (SEM) was performed on a LEO
1530 microscope equipped with InLens and Secondary Electron
detectors using low accelerating voltage (3 kV). Prior to analyses,
the samples were cryofractured and coated with a 3 nm layer of
palladium/platinum alloy in a Cressington 208 HR sputter-coater.
M
n,theor = conversion  ([S]0/[macroinitiator]0)  104.
d
Obtained from SEC equipped with RI detection (PS standards) eluting with THF
as the mobile phase.
Conversion as determined by gravimetry for ATRP of styrene initiated by the
e
initiator 1.
decreased when the initial ratio of monomer-to-initiator concen-
trations increased. The as-obtained PLA precursors were character-
ized by 1H NMR. The spectra displayed the typical chemical
displacements of PLA characterized by broad resonance bands at
5.10–5.30 and 1.40–1.60 ppm corresponding respectively to the –
CH– and –CH3 moieties of the repeating lactide units (Fig. 2). Other
characteristic peaks at 0.94 and 4.36 ppm arising from the aliphatic
protons of the initiator, i.e. butanol, were observed.
3. Results and discussion
3.1. Synthesis and characterization of functional diblock copolymers
PS-b-PLA diblock copolymers with a sulfonyl group at the junc-
tion between the two constituent blocks were generated through a
three-step sequential method (Fig. 1). Such
The presence of the
x-hydroxyl end group, which has a crucial
a methodology
role regarding the anchoring to the initiator 1, was evidenced by
the presence of a characteristic peak at 2.71 ppm. It was reacted
with the chlorosulfonyl group of the difunctional initiator 1 via a
condensation reaction to yield the corresponding brominated
PLA-based macroinitiator (3). For this purpose, the reaction was
set up for 48 h in different experimental conditions so as to maxi-
mize the conversion yield. The non-reacted free initiator 1 was
eliminated by precipitation of the macroinitiator 3 in diethyl ether.
required the utilization of an asymmetric difunctional initiator that
enables the creation of both blocks from different orthogonal func-
tionalities of the initiator. For this purpose, we specifically pre-
pared an aromatic initiator molecule (1) containing a potential
sulfonic acid functionality within its structure and two different
functional end groups, i.e. a chlorosulfonyl moiety and a tertiary
bromide (step 1). Such an initiator was thus able to react with a
x
-hydroxy PLA (2), previously prepared, by condensation between
Yet, a part of
x-hydroxy PLA 2 was also present along with the
the terminal hydroxyl group from PLA and the chlorosulfonyl
group of the initiator 1 (step 2), while ATRP of styrene was pro-
moted via the homolytic cleavage of the carbon-bromine bond of
the as-obtained PLA macroinitiator 3 (step 3).
The PLA precursors (2a, 2b, 2c) were produced by ROP of D,L-
lactide initiated by butanol, and they were obtained with low to
moderate molar masses (Mn(SEC) ranging from 4600–10,000
g molÀ1). It is noteworthy that the PDI values of the PLA polymers
increased with increasing their molar masses (Table 1). This clearly
indicated that the degree of control over the ROP of D,L-lactide
macroinitiatior product, and could not be removed before the
following ATRP step.
The functionalization rate was calculated from the 1H NMR
spectra of the macroinitiators (Fig. 3, as an example) by using the
ratio between the signal intensities associated with the doublet
of the initiator moiety at 7.87 and 7.94 ppm and the characteristic
broad bands due to the –CH– group of the repeating lactide units at
5.1–5.2 ppm. The main features of the
x-bromo PLA macroiniti-
ators (3) are gathered in Table 2.

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R. Majdoub et al. / Reactive & Functional Polymers 72 (2012) 495–502
The ATRP process of styrene triggered by these macroinitiators
order to develop a morphology of hexagonally close-packed cyl-
inders of PLA cylinders surrounded by a PS matrix (Table 3). In a
previous contribution [19], Hillmyer’s group has thoroughly
investigated the equilibrium phase diagram of PS-b-PLA with
low PDI values. However, our synthesized samples displayed
rather broad molar mass distributions. This might be ascribed
not only to the relatively high polydispersity indices of PLA pre-
cursors (1.2–1.4), but also to a difficult control over styrene
ATRP from the brominated PLA macroinitiators. The styrene
homopolymerization using the initiator 1 was monitored as a
model study to investigate whether the ATRP process was pro-
ceeding in a controlled manner under the selected experimental
conditions (Table 4). High PDI values as well as experimental
molar masses higher than the theoretical ones clearly indicated
a rather low degree of control, probably due a slow dynamics
of exchange between active and dormant species.
was carried out in typical experimental conditions using CuBr/
PMDETA as the catalytic system. The effective formation of the
PLA-b-PS diblock copolymers (4) was verified by a combination
of 1H NMR spectroscopy and SEC. First, the 1H NMR spectra of
PLA-b-PS copolymers were consistent with the expected struc-
tures, especially with the appearance of broad peaks at ꢀ6–7 and
1.41–1.84 ppm that corresponded respectively to the aromatic
and aliphatic protons of PS (Fig. 4, as an example). Furthermore,
Fig. 5 displays the typical SEC traces obtained for a PLA macroini-
tiator and the corresponding PLA-b-PS copolymer. All SEC chro-
matograms of copolymers exhibited monomodal distributions
and a shift of the peaks toward lower retention times, thus
confirming the formation of diblock copolymers.
It is noteworthy that the diblock copolymers were formed
with a PLA volume fraction (fPLA) ranging from 0.27–0.41 in
Loading direction
« channel die »
Constraint
direction
1 mm
60 mm
Flow direction
3 mm
Fig. 6. Schematic representation of a home-made channel die used to align the nanodomains in the diblock copolymers.
Fig. 7. 2-D SAXS patterns of PLA-b-PS copolymers oriented by channel die processing (pattern recorded parallel to the flow direction) and corresponding radial profiles of
scattering intensity relative to (a) PLA46-b-PS46 (4a), (b) PLA96-b-PS91 (4b), and (c) PLA154-b-PS240 (4c) copolymers.

R. Majdoub et al. / Reactive & Functional Polymers 72 (2012) 495–502
501
Fig. 8. 1H NMR spectra of (a) PLA96-b-PS91 (4b) after hydrolysis of the PLA block, (b) 2-methoxyethylamine, and (c) resulting PS matrix upon reaction of the SO3H chain-end
groups with 2-methoxyethylamine.
Fig. 9. Cross-sectional SEM micrographs of the porous polymeric material obtained from PLA96-b-PS91 (4b) after channel die processing and hydrolysis of the PLA sacrificial
block.
3.2. Macroscopic orientation of diblock copolymers
the flow direction. Obviously enough, for the diblock copolymer
with the highest molar mass, the isotropic halo observed in the
2-D pattern attested the absence of any orientation on a large scale.
The rather high PDI values associated with the PLA-b-PS diblock
copolymers might account for this material inhomogeneity as sev-
eral recent reports have discussed how broad molar mass distribu-
tions in diblock copolymers influence interfacial curvature and
domain spacing, and eventually have a significant impact on their
overall phase behavior [8,9,21–23].
The macroscopic orientation of copolymer nanodomains in bulk
materials was realized through a channel die processing [20]. Dur-
ing this procedure, diblock copolymers were subjected to shear
flow that induced a stress in the materials. This shear stress could
then be relieved by a rearrangement of copolymers in such a way
that the nanodomains might orient along the shear direction as
shown in Fig. 6.
Fig. 7 displays the 2-D SAXS patterns (for the first-order scatter-
ing qà peak) and the corresponding radial profiles of scattering
intensity for the investigated PLA-b-PS copolymers. For the
PLA46-b-PS46 sample, we observed an intense and anisotropic halo,
and a domain spacing of 19 nm could be determined from the
radial profile, while two scattering spots were detected for the
PLA96-b-PS91 specimen and a domain spacing equal to 37 nm was
estimated. Even though these patterns indicated the occurrence
of some degree of orientation in the channel die-processed copoly-
mers, they did not permit to identify the cylindrical morphology
expected for these structures. Yet, the PLA96-b-PS91 pattern corre-
sponded to a column-like structure with oriented domains along
3.3. Generation of functionalized nanoporous polymeric materials
Under mild alkaline conditions, functionalized nanoporous
polymeric materials were obtained by selective and quantitative
hydrolysis of the minor sacrificial block (PLA) in channel-die pro-
cessed PS-b-PLA block copolymers. The completion of this hydro-
lytic process was checked by 1H NMR through the total
disappearance of the characteristic broad bands associated with
PLA at 5.20 ppm (signal assigned to –CH– motif of lactide repeating
units in Fig. 8).

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R. Majdoub et al. / Reactive & Functional Polymers 72 (2012) 495–502
Scanning electron micrographs of the resulting materials
supports or scaffolds for nanomaterial synthesis, as well in the area
of advanced separation techniques as selective membranes.
revealed nonoscale porous structures, as observed in Fig 9. It is
worth mentioning that the higher the molar mass of the PLA block,
the larger the pore diameters (data not shown). In addition, the
presence but more importantly the accessibility of the sulfonic acid
functionality displayed at the surface of the porous polymeric
materials was highlighted by a post-modification reaction. Experi-
mentally, sulfonic acid groups (SO3H) were activated in a first step
with thionyl chloride to provide the corresponding chlorosulfonyl
Acknowledgements
The authors thank the ‘‘Groupe Chimique Tunisien’’ for provid-
ing R.M. with a Grant. They are also indebted to the CNRS, the
Université Paris-Est Créteil and Sfax University for allowing travel
exchanges between France and Tunisia. Moreover, they are thank-
ful to Dr. P. Davidson (Orsay, France) for his kind cooperation in
SAXS analyses.
(SO2Cl) groups which were reacted in
a second step with
2-methoxyethylamine, thus leading to the formation of sulfon-
amide functions: end group functionalization efficiency close to
100% was determined by 1H NMR (Fig. 8). This chemical reaction
demonstrated that the chemical functionalities of the nanoporous
materials are accessible and modifiable, and are not sterically hin-
dered within the PS matrix. The presence of such tailored function-
alities at the pore interface is very important regarding the
potential applications of these nanoporous frameworks as catalytic
supports or scaffolds for nanomaterials synthesis for instance.
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We have reported on an original route to novel functionalized
nanoporous materials through the use of nanostructured PLA-b-
PS diblock copolymers with a sulfonyl group at the interface
between the two distinct blocks. Such copolymers can be success-
fully synthesized by a three-step sequential approach starting from
a purposely designed asymmetric difunctional initiator. The post-
modification of the sulfonic acid functionality that line the pore
walls can be achieved with a model amine compound, which re-
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the substances that can be drawn into the voids. Our research ef-
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acid-functionalized nanoporous materials for diverse applications
but also to the tuning of the chemical functionality positioned at
the junction between both blocks of copolymer precursors.
These polymer-based nanoporous materials have expected po-
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